


AMERICAN SOCIETY OF CIVIL ENGINEERS. 

INCOKPORATED 185 2. 



THE STRE]ST.TH AND 

OTHER PROPERTIES OF MATERIALS OF CONSTRUCTION, 

AS DEDUCED FROM STRAIN DIAGRAMS AlTOMATIt'ALLV rRODlCED BY 

THE AUTOGEAPHIC RECOKDING TESTI:N^G MACHINE. 

A Paper by Prof. Eobekt H. Thukstox, Member of the Society. 
Peesexted December 31st, 1875. 



In a pai^er read before the Society in February and April, 1874,* the 
u-riter gave an account of a series of researches which he had made with 
a novel form of apparatus, and illustrated the work by fac-similies of a 
collection of automatically produced strain-diagrams. The new method 
of investigation adoi^ted and the importance of some of the conclusions 
deduced from the autogTaphic records have attracted much attention and 
the paper has been extensively republished, f It has recently been trans- 
lated into the German for Dingler's Polytechuisches Journal, and its 
pubhcation has been followed by a X3aper by a distinguished colleagTie of 
the writer, Prof. Kick, J of the Institute of Technology at Prague, who 
makes a number of criticisms^ which indicate that it may be advisable to 
consider some of the more obscure i^oints in the original paper at greater 
length and to exhibit the sources of the errors which have been com- 
mitted by the critic. 

The first criticism made by Prof. Kick, as will be seen by a perusal of 
the pajDer, a translation of which is herewith given, || is a statement that 
important discrepancies exist between the results obtained exj)erimentally 



* Transactions, Vol. II, page 349; Vol. Ill, page 1; t Journal of the Franklin Institute, 1874; 
Van Nostrand's Mag., 1874; Dingler's Polytechnic Journal, etc., etc., 1875; + International 
Jury, Vienna, 1873 ; § Kritik Uber R. H. Thurston's untersuchen uber festickeit und elas- 
ticitat der constructions; Materialen Von Friedrich Kick, Bd. 218, H. 3. 

!l Criticism of R. H. Thurston's '• Researches on the Strength and Elasticity of 
THE Materials of Construction," by Friedrich Kick.— Translated from Dingler's Poly- 
technisches Journal ; Band 218, H. 8. 

The results of Thurston's investigations of the strength and elasticity of materials, no less 
than the ingenious deductions therefrom, require the more thoroiigh examination because 
of the important discrepancies arising between those results and the experiments instituted 
by myself for the determination of the relations of tensile and compressive forces as influ- 
enced by changes of form. 



/{% 



A 






by the author of the criticism and by the writer. This difference is at- 
tributed to an assumed peculiarity of the apparatus and of the method of 
experiment adopted by the writer, which is asserted to produce serious 
errors. That such a difference does appear between the results obtained 
by the writer and the critic is undoubtedly the fact ; that they are at- 
tributable to the cause assigned is less evident, and what follows may 
prove the assertion entirely unfounded. The critic makes an assumption 
of faulty manipulation mthout evidence of its existence and then claims 
to "prove" mathematically that the apparatus, which is asserted to be 
"dynamic" in its action, records its results statically and thus intro- 
duces fatal errors of record. 

The mathematical portion of the paper is correct, and we will take 
advantage of that fact and will show how far the adverse element — the 
resistance due to the acceleration of weight — which is so boldly asserted 
to be the cause of "serious" errors, is likely to introduce such errors. 

Taking an extreme case, supposing a perfectly rigid test-piece to 
be under test, the velocity of motion of the weight would be precisely 
equal to that of the handle and would be a maximum. Actually, the 
test-piece always yields and the velocity of the w^eight is invariably less 
than that of the handle. In the greater number of cases, the weight 
moves with much less rapidity than the handle, even when moving at 
its highest rate of speed, and during the greater part of the test, the 
rate of motion of the weight is so low as to be imperceivable and inca- 
pable of measurement, and at other times, the weight actually moves 
slowly downwards, as is seen by reference to the published strain-dia- 
grams, on which the relative motion of weight and handle can be readily 
determined. 

The motion of the weight is, in fact, independent of that of the handle 
and varies with the resistance of the test-piece, rising or falling as that 
resistance increases or diminishes, always slowly and almost invariably 

The study of Thurston's treatise indicated that a certain error, sometimes insignificant, 
sometimes important, was inherent in the results, the source of ^Yhich was to be found in 
Thurston's testing machine. This machine, acting dynamcally, records its results as if they 
were statical, the greater the velocity adopted, the greater is this error. This assertion is proven 
as follows : 

If a weight be suspended by a spring, when equilibrium occurs— whether for rest or mo- 
tion—the tension of the spring is proportional to the weight. As soon, however, as accelera- 
tion takes place, in the case of transition from rest to motion, as well as with varying velocities 
during motion, the tension on the spring must change; this variation may be expressed by the 
variation of S In expression 

for uniformly accelerated motion, in which S is the tension on the spring ; v is the velocity at 
the end of the time t, and g is the acceleration of gravity =9. 808 M. 



witli very much less velocity than that of the handle. In making- 
tests vidth this machine, the handle is always moved very slowly, and 
when attempting to secure diagrams for scientific purposes especial pre- 
caution is taken. 

The following figures represent the rate of motion of the handle, meas- 
ured alternately for a somewhat rapid and for an ordinarily slow motion. 
The motion of the weight is, as has been shown, veiy much slower. 





Time. 


Angle. 


E. Cos. 


Space. 


Max. Moment. 


M) 


1 Min. 


16°.00. 


47.125 in. 
1.197 m. 


13.54 in. 
0.362 m. 


135.987 ft. lbs. 


(B) 


2 Min. 


STo.ee 


38.75 in. 
0.984 m. 


32.00 in. 
0.813 m. 


292.755 


(cri 


1 Min. 


16=^.00 


47.125 in. 
1.197 m. 


18.54 in. 
0.362 m. 


135.987 " 


(D) 


1 Mill. 


37=.06 


39.00 in. 
0.996 m. 


31.70 in. 
0.805 m. 


291.70 



Where the effort was made to attain gTeater rapidity of motion, the 
following results were obtained : 





Time. 


Angle. 


E. Cos. 


Space. 


Max. Moment. 


(E) 


1 Min. 


33°.66 


40.75 in. 
1.035 m. 


28.78 in. 
0.761 m. 


267.02 ft. lbs. 


(f) 


1 Min. 


47=. 66 


33.00 in. 
0.838 m. 


40.63 in. 
1.032 m. 


350.98 " " 



0.1 M. 


0.4 


2.0 


0.2 


0.5 


3.0 


0.3 


1.0 


4.0 



. 


G. 


> 


1.01 


1.04 


1.20 


1.02 


1.05 


1.30 


1.03 


1.10 


1.40 



Let t = 1 second, and let v have the following successive values for the corresponding 
values of S, and the value of G will be : 

0.05 M. 0.20 1.00 

0.10 0.25 1.50 

0.15 0.50 2.00 

Thus, even when the increase due to uniform acceleration amounts to but 1 m. per second, 
the tension will be 20 per cent, greater than in the case of equilibrium. 

Let us apply this investigation to the Thurston machine in which tests are made by torsion. 
By depressing the lever C, B rises, the axes of both being united by the test-piece lying in the 
jaws. (For description of the machine, see Transactions, Vol. II, page 350, &c.. Translator.) 

We may liken this apparatus to a balance to which has been added an automatic recording 
apparatus "which records the constantly increasing pressures exerted upon the lever C, and 
which are transmitted to the wei-hted lever B by means of the test-piece. These records can 
only be based upon statical laws ; for Thurston actuates a movable recording-pencil, attached 
to the weighted arm by a fixed and invariable guide-curve which can only be constructed by 
reference to the statical moments of the weight D. 

Neglecting unavoidable sources of error which are present in all automatic recording ap- 
paratus, this has one gi-eat defect. 



Prof. Kick states correctly the resistance due to acceleration of tlie 
motion of the weight as equal to ^, and the total amount of stress as 

^-'^+irf •' (1) 

in which expression, S= the total stress, v = the acquired velocity at the 
end of the time ^, G=the weight and g = the acceleration of gi-avity 
= 32i feet = 386 in. = 9. 8 m. 

G=^ + JJ (2) 

Then, for the several cases just given, assuming the velocities to be those 
of the weight, as improperly asserted by Prof. Kick, we get : 

(A.) 

(B.) 
(C.) 



s 

G 


^ gt '^^ 386X60 -1-001212 


S 

G 


32 y 9 
"^+386X120 -1001401; 


S 

G 


-^ + ll^-"01-;. 


S 
^G 


^ + Sira- 1-001347; 



(D.) 

And for those cases in which the rate of acceleration was made as great 
as could be obtained by the exertion of aU the strength of the operator : 

(F) ^-14- 40-68X2 ^ __ 



It is constructed upon the basis of statical relations. In using the machine, equilibrium 
does not exist, but motion. The diagrams must therefore deviate the more from the truth, 
the more suddenly and the more rapidly the lever C is moved. If. therefore, the greatest care 
IS not taken in experimenting, using low velocities and a steady hand, the diagrams will be in- 
correct and entirely untrustworthy for strictly scientific researches. No proof is required to 
show that the same force is required to produce the same acceleration, whatever the position 
of the lever carrying the weight at the beginning of the acceleration. 

The moment of the force producing acceleration must be added to, or subtracted from, the 
moment of the weight D, according to the direction of the motion. Only the latter is graph- 
ically recordcd-the former is not. The error thus arising would be constant for a uniform 
acceleration and could be corrected by drawing a line parallel to the curve, were it possible to 
move the lever C with a uniform acceleration. But. since this cannot be done by hand, such a 
rectihcatiou of the graphical record of the Thurston machine cannot be made 

Further, we have : that the above-given quantity which is to be added or subtracted is 
relatively of greater influence, the less the torsional moment of the weight D; in other words 
the errors of the diagram due to the movement of the weight are of most importance at the 
initial portion of the diagram, within the elastic limit. 

It is possible that the peculiar forms of the diagrams 6, 10 and 8,5, Plate B [Plate II, Vol. II 
page 378). which are convex to the axis of abscissas, are a consequence of the more rapid motion 
of the hand-lever during those experiments, and, as well as the irregularities of the lines of 
the diagrams, may be partly explained by this dynamic action of the machine 

When. thc,refore. Thurston says : •• (1.) To determine the homogeueousness of the mate- 
nal, examine the form ol the initial portion of the diagram between the starting point and the 



It is seeu from the above that the maximum possible errors, due to 
the cause assumed by tlie critic as the source of the discreiDaucies which 
he has found to exist bet^veen his work and the self-recorded results 
given by the autographic machine, are necessarily some fraction of one- 
eighth of one per cent. Every experienced investigator in this depart- 
ment of scientific research knows, however, that this limit of error falls 
far within the limit of variation of quality of every material of construc- 
tion, even when nominally of the same grade. The criticism is therefore 
seen to have no practical weight. 

Now, determining the relative motion of handle as given above, and 
of the weight, from the strain diagTams published, and taking wrought 
iron as the best illustrative example, it will be seeu that, within the elas- 
tic limit, the error claimed to destroy the value of the data secured may 
possibly amount to O.OUl, and that at the limit of elasticity even this error 
entirely disapi^ears, since the weight there ceases rising. Beyond the 
limit of elasticity, the error is that due to a rise of the weight equal to an 
exceedingly minute fraction of the motion of the handle, and is so small 
that it would be quite im^Dossible to detect it on the diagram by any 
method of measurement in use. The criticism of the distinguished 
author of this "-Jcritik^is thus seen to be quite insufficient to account 
for the discrepancies noted by him. He is quite right in looking for the 
source of error in the machine — provided that the results of the writer 
are eiToneous and those of Prof. Kick are right — for, in the former, the 

sudden change of direction ■which has been shown to indicate the elastic limit. I^otice, also, the 
incliuation from the vertical, and compare it with the incliiiation of the elasticity-line. 

" A perfectly straight line, beneath the elastic limit, perfectly parallel with the elasticitjr- 
llne, shows the metal to be homogeneous as to strain; i.e., to be free from internal strains, 
such as are produced by irregular and rapid cooling, or by working too cold. Any variation 
from this Line indicates the existence, and measures the amount of, strain" (Vol. Ill, page 2). 
The first sentence, inconsequence of the inherent error in the apparatus, is, in general, incor- 
rect. 

An indisputable and convincing proof that Thurston's machine is inapplicable to scientific- 
Investigations is found in the diagrams 101 and, particularly, in 118, Plate C (Plate III, Vol. Ill, 
page 30). The diagrams show, at b, c and and at b' c', that a rapid increase of velocity is fol- 
lowed by a rapid sinking of the line. This must necessarily occur ; for the pencil of the 
registering apparatus, in consequence of the peculiarity of this construction, does not record 
that moment which is exerted in the acceleration of the weight of those parts which are set in. 
motion by the test-piece. 

But Thurston deduces from these diagrams a direct reply to the question : what is the rela- 
tion of the resistance of the test-piece to rapid or slow distortion ? He deduces, from the fall 
of the line of the diagram with the motion, that the resistance decreases as the velocity of 
Btrain increases. We have seen that this assertion is not confirmed by those diagrams. That 
Kirkaldy has reached the same conclusion may be duo to a similar misinterpretation of the 
results of experiment. If Thurston's diagrams could give a definite answer to the question, 
they would rather read— the resistance is independent of the velocity of distortion. 

Referring to the conclusions deduced by Thurston's incorrect method, it is remarkable to 
find it stated that : " To determine the resilience of the material within any aasiimed limit of 



6 

story is told by the macMne itself and cannot be attributed to errors of 
personal observation as may those existing in da'a acquired by the 
older methods of ref:earch. 

It may be safely asserted that the errors due to the inertia of the 
weight and to its acceleration may, by careful handling, be made as 
minute and as practically immeasurable as those due the same cause in 
the older forms of testing machines. Considering the facts, that the re- 
sults obtained by the older methods of testing are liable to errors arising 
from personal observation, while, in the method adopted by the writer 
in the autographic recording testing-machine they are automatically 
registered, it would seem that the advantage, in respect to accuracy, 
must be on the side of the new method. 

The writer believes the facts exhibited above to prove conclusively 
that the bold assertion of the foreign critic — -that with the greatest care 
these strain-diagrams are liable to be incorrect and untrustworthy — -is 
without real basis and is itself absolutely incorrect. 

The second criticism of Prof. Kick, in Avliich he suggests this assumed 
source of error to be the cause of the differences in the initial portions of 
diagrams (6, 101 and 85 of Plate II, Vol. II., page 378), which the writer 
attributed to peculiar conditions of molecular or mechanical structure, 
is not only invalidated by what has been shown above, but most conclus- 
ively by a large number of experiments made before and after the date 
of the original paper, in which the noted x)eculiarities were very marked, 
although the experiments were conducted with uniform precaution. The 
fallacy of the criticism is still further proven by the characteristic differences 



•extension, measure tlie area of the cui-ve up to tlie assumed limit. To determiue the total 
resilience, or the shock-resisting power, measure the total area of the diagram;" [Vol.111 
page 3). 

While, on the other hand, he concludes: " The rapidity of action, in the cases of shock, and 
where malerials sustain live loads, is a very important element in the determination of their 
resisting power ; not only for the reason given already, but because the more rapidly the metal 
is ruptured, the less is the resistance to rupture ;" ( Vol. Ill, page 15) . Since the last sentences 
which contradicts the former is incorrect, the former may be correct ; it remains, however 
Etill unproven. * 

Similarly unproven is the assertion : " The effect of repeated bending, or other form of 
strain, can be thus inferred from an examination of the strain diagram of the material, obtain- 
ing from a single experiment a determination hitherto pnly obtained by a long and tedious 
process of repeated distortion;" ( Vol. Ill, page 8). It is here quietly presupposed that the dia- 
gram of resilience up to the point of fracture, for the test-piece strained by torsion, record, 
Mso the amount of work done in case of fracture for all other kinds of strain. The proof of 
.this is wanting; it would be dijQticult to produce it. 

[The critic forgets, throughout his paper, that the quality of the material is the property 
which it is attempted to determine, not the relations ot the several kinds of strain.-— K. H. T.] 

Thurston mentions the fact that : " The phenomenon here discovered is an elevation of 
the limit of elasticity by a couliuued strain;" {Vol. TJI, page 12). This " discovery" has also, 



noted in the initial portion of the diagram where different metala 
are compared, as shown in the published diagrams of iron, steel, copper, 
tin, etc. Such differences could not possibly arise from the assumed cause. 

Professor Kick adduces as what he asserts to be "absolute i^roof " 
of the existence of the source of error above alluded to, the peculiar 
strain- liagi'ams, 101 and 118, Plate III. These show the rapid motion 
of the handle (not of the weight) to be followed by a fall of the 
weight and a drop of the pencil. This was attributed by the writer to 
a weakening of the metal by rapid distortion ; a conclusion which has 
been confirmed by a study of Kirkaldy's experiments with his tension 
apparatus, by many experiments since made by the writer A^dth the 
a.utograiDhic machine, by numerous experiments made by Com. 
Beardslee at the Washington Navy Yard with a tension machine having 
peculiar facilities for exhibiting this phenomenon, and especially by the 
experiments made on a very large scale on iron beams for targats, as 
described by Gen. Barnard in a paper read before the Society (Trans- 
actions, Vol. I, page 173), and referred to by the writer, in the discussion' 
at the Seventh Annual Convention (Vol. III., page 128). 

The eiTor into which the critic has fallen will be seen at once when it 
is noted that during this rapid motion of the handle and the distortion of 
the test-piece, produced by a heavy blow on the handle, the weight had 
no time to move and the drop of the weight succeeded the distortion, as 
is expHcitly stated in the original paper to be an evidence of the weak- 
ening which is a consequence of rapid distortion. This evidence would 
seem to l)e quite sufficient. But the experiment described by Gen. 



been made aud published bj- General Uchatius {Die Stahlbrovge, Vortrag. GeJiatten am 10 
April. 187J:, Wien.) m 1873, iu the following words : " In all metals which possess a consider- 
able degree of ductility, it is interesting to extend the investigation to the elastic limit. We 
thus learn that these metals attain their highest elasticity only when they are strained beyond 
the elastic limit to a certain point and are allowed to remain so for a time." •' This advantage 
has never, until now, been noted." 

Thurston's machine tests specimens for torsion and the extension of the external fibres, 
calculated from the angle of torsion, cannot be considered as the measure of the extension of 
the fibres by tensile tests, for two reasons : First, because a diminution of length of the 
torsion test-piece must occur, which is not measurable from the angle of torsion graphically 
recorded by the machine. Second, for the reason that the external fibres are reinforced and 
strengthened by the internal fibres, in consequence of their lateral cohesion, they being less 
affected. That elongations of C9 and even 120 per cent, are found in wrought iron can only 
find its explanation on pages 100 and 101— elongations which no wrought iron will give. 

If Thurston finds nothing remarkable in this, but stales that this elongation of fibre is 
proportional to the redui.tion of section noted with the standard testing-machines, it should 
be said, on the contrary, that it is entirely inadmissible, for the percentage of elongation to bo 
given any relation to the reduction of cross section. Robert Lane HaswcU has noted this 
already. If we pull apart a test-piece like that shown in the accompanying illustration [The 
eketch represents a pair of test-pieces, of which one, a b, is intact ; the other, a' b' , on th© 



s 

Barnard, to say nothing of those of Com. Beardslee, are certainly con- 
clusively corroborative. 

The exception taken by the critic to the principles (6) and (7) are fully 
met by the above and no more need be written on this point. 

In the paper here referred to, Prof. Kick goes on to state that the 
phenomenon of " elevation of the elastic Umit by strain," claimed ta 
have been discovered by the writer, was discovered by Gen. Uchatius. 
of Vienna, and published in April, 1874. [Die Stahlbronge Vortrag. 
Gehalten am 10 April, 1874, Wien. ) 

The writer is greatly pleased to find his work confirmed by so distin- 
guished an authority, but his own discovery of this remarkable and im- 
portant phenomenon was made months earlier, and was announced at the 
Annual Meeting of this Society, November, 1873, and formally placed on 
record in a "Note on the Resistance of Materials," read November 19th, 
1873. (Transactions, Yol. II, page 239. ) The phenomonon was also dis- 
covered by Com. Beardslee, U. S. Navy, soon after, and by an entirely 
independent method of investigation, and was made known by him be- 
fore the end of that year. It has since been observed by many experi- 
menters, but the writer has as yet met with no claim of priority of dis- 
covery. 

Prof. Kick asserts that the extensions estimated by the writer cannot 
be correct, because of a diminution of length in the specimen, and 
because of the influence of the cohesion existing between the inner and 
outer fibres of the mass. The writer can only say that experiment does 
not seem to confirm these assumptions and assertions. 

point of rupture at a point of largely reduced section. — Translator. ^ the greatest reduction of 

area will occur at the point of rupture, and at that point, also, is the greatest elongation. 

If we determine the percentage, or the extension by taking the greatest length, a b, 

immediately befoi-e rupture, and designate the proportion of elongation by the quotient,, 

a'b' — ab 

— ;- — , then, for the same material, very different values will be obtained^ according ta 
aft' > J JO 

the length a b, whereas, the amount of extension at the point of rupture, which is nearly 

the same in either long or short specimens, greatly changes the percentage of extension. 

It is easily seen that a large percentage of extension will be obtained with very short test- 
pieces than with long ones of the same material. The reduction of area, therefore, affords a 
means of measuring the ductility of the material, affording, however, no precise determina- 
tion of the percentage of elongation, which can only have a definite valae when taken within, 
the elastic limit. 

The theory of strength of materials is a department of mechanics in which the greatest 
care should be exercised la drawing conclusions; it Avould also seem to be better to admit this, 
where satislactory results are not obtained, than to enter with indefinite phrases into the 
realms of conjecture. 

In that part in which Thnrston treats of the eflect of temperature upon the resistance of 
materials, conclusions 1 to 9 (Vol. Ill, page 21) have no significance, and simply say, «« We do 
not know what is determined." The following sentences are not more valuable : (10.) That 



9 

In regard to the elongations given by the writer, amounting, ^^-ith 
some ductile materials, to 120 per cent. , it need only be repeated that it 
was explicitly stated that those figures are given as the best indication 
of the ductile quality of the material, that they are proportional to the 
maximum elongation of the most extended portions of the metal tested 
by tension, for the very reason stated in opposition by Prof. Kick, that 
the tension specimen invariably " necks down," and does not stretch 
as a whole, or uniformly ; and it was stated that these factors of exten- 
sion are related to the reduction of cross-section observed in tension, and 
are such as do occur within the elastic limit in homogeneous materials 
and such as would be observed were the material under tension, to draw 
down uniformly from end to end until fracture occurs, leaving the 
whole i^iece, in that case, of the diameter of the fractured section actu- 
ally observed in the tension experiments. 

The writer has stated his idea that the reduction of section by tension 
and not the extension of the whole specimen, is the most accurate meas- 
ure of the ductility of the material. After jDassing the elastic limit, and 
after " necking down" begins, the elongation of a test-piece under 
tension is a function of its diameter and not of its length ; and the whole 
extension may be expressed by the formula, E^Al-^-BId, an expres- 
sion which the ^\Titer has not yet met with in any work on this subject. 

The writer has noted these errors of the critic with as much sur^Drise 
as regret, and especially as he finds them associated with the very excel- 
lent caution against " roaming in the fields of conjecture" in such 
scientific work. 

Finally, comparing conclusions (10) and (11) with (19) and (20 ?) in 
which the effects of temperature are referred to, the critic notes an apparent 

the general effect of increase or decrease of temperature is, with solid bodies, to decrease or 
increase their power of resistance to ruptare, or to change of form and their capability of sus- 
taining dead loads. (11.) That the general effect of change of temperature is to produce 
change of ductility, and, consequently, change of resilience or power of resisting shocks and 
of carrying live loads. This change is usually opposite in direction, and greater in degree 
than the variation simultaneously occurring in tenacity. On the other hand: (19.) In pure and 
well-worked metals, decrease of temperature is accompanied by an increase of strength as 
well as an increase of elasticity and resilience. The last statement is evidently contradictory 
of conclusion 11. Which is now correct? 

With the great care which we know to have been taken in the translation, these inconsist- 
encies must be from the original, which we have not at hand. We are the more certain of this 
from the fact that other discrepancies exist, which, from appearances, could only have been 
transferred from the original, although they are of comparative insignificance. 

In these opposing statements, the value of the Thurston machine is not contested for 
practical purposes. In many cases the diagrams recorded by this undeniably simple apparatus 
have contributed to the confirmation of tests of resistance of materials, and the merit of 
Thurston is decided and indisputed. 



10 

discrepancy which a more careful reading would have explained and the 
necessity of reference to them, perhaps, not have arisen. It is not, how- 
ever, impossible that the writer was not sujBBciently explicit. Eeferring 
to the original paper, it will be seen that the author quotes from an 
earlier monograjph on the effects of temperature in which all of the 
earher researches of both physicists and engineers, so far as they were 
accessible to him, were collated, and the conclusions, derived by com- 
parison, were that a rise of temperature decreases the resisting power of 
materials while increasing their ductility and sometimes their resilience ; 
a decrease of temperature seemed to produce the opposite effect. The 
generally conflicting testimony of those who, on the one hand, had ex- 
perimented by steady stress, and those who, on the other hand, had expe- 
rimented by shock, thus seemed to be reconcilable. The apparent dis- 
crepancies between authorities were concluded to be due to differences 
of method similar to those which are claimed by Prof. Kick to distinguish 
the researches of the writer from those of the better known authorities, 
— but with more reason. 

Subsequently the invention of the autographic testing machine 
having, for the first time, furnished a means of making simultaneous 
determinations of the several mechanical properties of the test-piece, the 
real facts seemed to be proven to be slightly different, and as stated in 
(20) that with pure well-worked metals the principle enunciated in (28) 
is fully illustrated, and a decrease of temperature is accompanied by 
an increase of strength, ductility and resilience ; (21) that materials 
which are impure and irregular in character may exhibit exceptions to 
and even reversals of that principle in changes of ductility, and, while 
increasing in power of resisting simple stress, may, by a diminution of 
temperature, lose their power of resisting shocks ; and that the effect 
of change of temperature probably varies with the character of the 
material. 

The writer is grateful for the pleasant compliment contained in the 
closing paragraph of the paper of Prof. Kick, and trusts that the above 
remarks may indicate that the ordinarily useful work of the confessedly 
valuable addition to " practical" testing apparatus, which has been found 
in the autographic recording testing machine may prove to be sup- 
plemented by not less valuable scientific work. 



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